In 1967, Veselago postulated theoretically an electromagnetic complex material in which both permittivity and permeability were assumed to have negative real values, and he analyzed plane wave propagation in such a medium, which he called a “left-handed (LH)” medium [V. G. Veselago, “The electrodynamics of substances with simultaneously negative values of ε and μ,” Soviet Physics Uspekhi, Vol. 10, No. 4, pp. 509–514, 1968 (in Russian Usp. Fiz. Nauk, Vol. 92, pp. 517–526, 1967]. According to Veselago's analysis, in such a “double-negative (DNG)” material [R. W. Ziolkowski, and E. Heyman, “Wave propagation in media having negative permittivity and permeability,” Phys. Rev. E., Vol. 64, No. 5, 056625, 2001], the Poynting vector of a plane wave is antiparallel with its phase velocity. In recent years, Shelby et al. in an article entitled “Experimental verification of a negative index of refraction,” Science, vol. 292, no. 5514, pp. 77–79, 2001, inspired by the work of Pendry et al. in articles entitled “Magnetism from conductors and enhanced nonlinear phenomena,” IEEE Trans. Microwave Theory Tech, Vol. 47, No. 11, pp. 2075–2081, November 1999, and “Low-frequency plasmons in thin wire structures,” J. of Physics: Condensed Matter, Vol. 10, pp. 4785–4809, 1998, reported the construction of a composite medium in the microwave regime by arranging arrays of small metallic wires and split ring resonators. The anomalous refraction for this medium was demonstrated in the afore-mentioned Shelby et al. article and in the following articles: D. R. Smith, et al., “Composite medium with simultaneously negative permeability and permittivity,” Phys. Rev. Lett., Vol 84, No. 18, pp. 4184–4187, 2000; and R. A. Shelby, et al., “Microwave transmission through a two-dimensional, isotropic, left-handed metamaterial,” Appl. Phys. Lett., Vol. 78, No. 4, pp. 489–491, 2001. Various aspects of this class of metamaterials are now being studied by several groups worldwide, and many ideas and suggestions for potential applications of these media have been mentioned.
For example, the present inventors have suggested the possibility of having thin, sub-wavelength cavity resonators in which a layer of the “double-negative” (DNG) medium is paired with a layer of conventional material (i.e., a “double-positive (DPS)” medium) in articles entitled: N. Engheta, “An idea for thin subwavelength cavity resonators using metamaterials with negative permittivity and permeability,” IEEE Antennas and Wireless Propagation Lett., Vol. 1, No. 1, pp. 10–13, 2002; N. Engheta, “Guided waves in paired dielectric-metamaterial with negative permittivity and permeability layers” URSI Digest, USNC-URSI National Radio Science Meeting, Boulder, Colo., Jan. 9–12, 2002, p. 66; and N. Engheta, “Ideas for potential applications of metamaterials with negative permittivity and permeability,” Advances in Electromagnetics of Complex Media and Metamaterials, NATO Science Series, (editors S. Zouhdi, A. H. Sihvola, M. Arsalane), Kluwer Academic Publishers, pp. 19–37, 2002. As explained in these articles, theoretical results have revealed that a slab of DNG metamaterial can act as a phase compensator/conjugator. Thus, by combining such a slab with another slab made of a conventional dielectric material one can, in principle, have a 1-D cavity resonator whose dispersion relation does not depend on the sum of thicknesses of the interior materials filling this cavity, but instead it depends on the ratio of these thicknesses. The inventors later extended this work to the analyses of parallel-plate waveguides containing a pair of DPS and DNG layers, guided modes in open DNG slab waveguides, and mode coupling between open DNG and DPS slab waveguides. In each of these problems, the inventors found that when a DNG layer is combined with, or is in proximity of, a DPS layer interesting and unusual properties are observed for wave propagation within this structure. Indeed, the paired DNG-DPS bilayer structures were found to exhibit even more interesting properties than a single DNG or DPS slab—properties that are unique to the wave interaction between the DNG and DPS layers.
By exploiting the anti-parallel nature of the phase velocity and Poynting vectors in a DNG slab, the present inventors theoretically found the possibility of resonant modes in electrically thin parallel-plate structures containing such DNG-DPS bilayer structures. Following those works, a first set of preliminary results and ideas for the guided modes in a parallel-plate waveguide containing a pair of DNG and DPS slabs was presented by the present inventors. Later, in an article entitled “Anomalous mode coupling in guided-wave structures containing metamaterials with negative permittivity and permeability,” Proc. 2002 IEEE-Nanotechnology, Washington D.C., Aug. 26–28, 2002, pp. 233–234., the present inventors showed the effects of the anomalous mode coupling between DNG and DPS open waveguides located parallel to, and in proximity of, each other. Some other research groups have also explored certain aspects of waveguides involving DNG media.
Most of the work in the area of metamaterials reported in the recent literature has so far been concerned with the wave interaction with DNG media, either by themselves or in juxtaposition with conventional (DPS) media. However, as will be explained in more detail below, the present inventors have now recognized that “single-negative (SNG)” materials in which only one of the material parameters, not both, has a negative real value may also possess interesting properties when they are paired in a conjugate manner. These media include the epsilon-negative (ENG) media, in which the real part of permittivity is negative but the real permeability is positive, and the mu-negative (MNG) media, in which the real part of permeability is negative but the real permittivity is positive. For instance, the idea of using such a combination to provide an effective group velocity that would be antiparallel with the effective phase velocity, and thus acting as an effective left-handed (LH) medium has been explored by Fredkin et al. in “Effective left-handed (negative index) composite material,” Appl. Phys. Lett., Vol. 81, No. 10, pp. 1753–1755, 2 Sept. 2002.
The present application addresses the characteristics of ENG-MNG bilayer structures, such characteristics including resonance, complete tunneling, transparency, and guided modes. Such bilayer structures are the subject of the present invention.